EP 2 233 309 A2 discloses an ink composition containing water in an amount of 20-90 weight % based on the total weight of the ink, a pigment and a resin, which may be a water dispersed resin (i.e., a latex). WO 2011/021591 discloses an inkjet ink containing a water-dispersible colorant, a water-soluble organic solvent, a surfactant, a penetrant, water and preferably a water dispersible resin. Both mentioned prior art documents disclose methods for printing said inks onto media normally used in process printing or offset printing (e.g., machine coated (MC) or off-set coated media).
In a highly productive inkjet printing it is preferred to obtain (almost) instantly dry and robust prints, which can be handled at high speed and stay undamaged during transport from a printing module to further process equipment, for example to a fuser station in the printer.
A disadvantage, of known aqueous ink compositions is that they exhibit too low of a drying speed and/or require relatively high fuse energies to be suitably used in a highly productive inkjet printing process.
A disadvantage of known aqueous ink compositions comprising dispersed components (e.g., a dispersed resin and/or dispersed dyes or pigments) is that such ink compositions, in particular when used in highly productive inkjet printing, need to contain a substantial non-evaporating or hardly evaporating dispersion-stabilizing polar fraction (e.g., 20 weight % or more relative to the total ink composition) of water soluble organic cosolvents, usually aliphatic polyhydric alcohols having a relatively low vapor pressure to provide reliable jetting and cleaning behavior of the inkjet printing devices (print heads). Such a non-evaporating or hardly evaporating dispersion-stabilizing polar fraction may, depending on the nature of the medium to be printed on, have a negative influence on the drying speed of a print and/or the required fuse energy. It may therefore be beneficial to print quality and robustness to provide an ink composition having a more specific drying and/or fuse behavior. In particular, when intended to be used in a highly productive inkjet printing process, an ink composition having a higher drying speed and relatively low required fuse energy is preferred.
Alkylene or dialkylene glycol mono- and di-ethers (e.g., propylene glycol mono-methyl ether) are commonly used as a cosolvent in the ink formulations to tune the drying behavior, sometimes in combination with heating (˜50° C.) of the medium during printing. However, the choice of suitable cosolvents from this class of glycol ethers is limited, partly because of high HS&E (i.e., Health, Safety and Environmental) risks.
It is therefore an object of the present invention to provide an aqueous ink composition having an improved drying and fuse behavior, without compromising the print quality and print robustness to an unacceptable extent.
It is another object of the present invention to provide an aqueous ink composition comprising dispersed components and having an improved drying and fuse behavior, without compromising the dispersion stability of the ink composition and the print quality and print robustness to an unacceptable extent.
It is yet another object of the present invention to provide an aqueous ink composition with low and in particular negligible HS&E risks.